A number of cationic organic water treatment additives have been developed for various applications in industrial water systems. For example, cationic biocides, or quaternary amine compounds (quat) have been developed for use in water treatment for suppressing the growth of microorganisms including, for example, fungus, mold and bacteria. These compounds contain, for example, a protonated nitrogen or phosphorus atom bound to hydrophobic alkyl and aryl groups, and work like soaps or detergents in disrupting the osmotic equilibrium of living cells. Deactivating or otherwise neutralizing these cationic biocides or quat can be desirable prior to discharging the treated water via blowdown or other process.
Compounds, such as anionic surfactants, have been developed for deactivating or otherwise neutralizing the active or toxic form of quat (“free” quat) before the treated water is discharged. However, existing methods are severely limited in that there is no way to know whether the anionic surfactants are effective. This is because existing tests only measure total quat and not the free or active form. Thus, a test might show too much quat because it also picks up the inactive from in the system, regardless of whether the inactive form might still exist. In order to apply these treatments efficiently and/or monitor the effectiveness of a cationic biocide remediation program, a fast and accurate method for determining the concentration of the free quat residual in the water stream would be of particular benefit.
Few reliable methods currently exist for the detection and quantification of quat. For example, the Hach QAC Method (8337 Direct Binary Complex Method) uses two reagents and is very difficult to administer and is subject to inaccuracies resulting from, for example, noise from cloudy water. It also suffers from much interference that makes rapid and accurate measurements of quat residuals difficult. Moreover, existing methods often suffer from interference associated with common ions including, for example, calcium, chlorine, magnesium and iron. Other compounds that can interfere with detection and quantification of quat include compounds associated with common surfactants and treatment compounds such as, for example, sodium lauryl sulfate and sodium polyphosphate. A chart reflecting some of these known interferences is provided below in Table 1. These interferences limit the usefulness of such methods, particularly when the goal is to perform rapid and accurate measurements of quat.
Interfering substanceInterference levelCalcium (as CaCO3)Positive interference above 1350 mg/LChlorine, HOCl andPositive interference above 7 mg/LOCl−Cyanuric acidNegative interference above 70 mg/LIgepal ™ nonionicPositive interference above 3 mg/LsurfactantIodine, I3−Positive interference above 3 mg/LIron, Fe3+Positive interference above 80 mg/LLiquimine ™ 14-P,Positive interference above 1825 mg/Lfilming amineMagnesium, Mg2+Positive interference above 1350 mg/LNiaproof ™ anionicNegative interference above 11 mg/LsurfactantPolyacrylic acidNegative interference above 16 mg/LSodium lauryl sulfateNegative interference above 8 mg/LSodium polyphosphatePositive interference above 1325 mg/LTribenzylaminePositive interference above 7 mg/LTriton X-100 ™Positive interference above 4 mg/Lnonionic surfactantUreaPositive interference above 8 mg/LHighly bufferedMay exceed the buffering capacitysamples or extremeof the reagents and require sample pretreatment.sample pHAdjust the sample pH between 3 and 5 byusing a pH meter or pH paper andadding dropwise an appropriate amountof acid or base such as 1.0N Sulfuric AcidStandard Solution or 1.0N Sodium HydroxideStandard Solution. If significant volumes ofacid or base are used, a volume correctionshould be made.
Another conventional method is high pressure liquid chromatography (HPLC). HPLC enables the dissection of complex mixtures into individual constituents. However HPLC measures total quaternary amine compound and is not able to measure only the amount of the quat that is free (unbound) in solution.
The ability to determine the concentration of the unbound free quat is desirable, as is the ability to distinguish between bound and free quat concentrations within a sample. Bound quat is that portion of the cationic quaternary amine compound that is strongly bound to a corresponding anionic compound and, therefore, exhibits significantly reduced antimicrobial activity compared to free quat present in the system. For example, the positively charged ammonium cation of the quat can be counter-balanced by a strong anion which renders the quat inactive. Existing methods only measure total quat and cannot distinguish between bound and free quat. Further, no automated on-line system currently exists for the detection, measurement and control of residual quat, or for the measurement and control of other cationic organic water treatment additives.
These and other issues are addressed by the present disclosure. It is an object of this disclosure to provide novel systems and methods for the fast and accurate quantification of the concentration of these cationic organic water treatment additives and, in particular, active forms of the additives within an aqueous stream as well as novel systems and methods for utilizing this improved quantification for detecting, measuring and controlling cationic organic water treatment additive residuals in industrial water systems.
One advantage of the present disclosure over existing methods for the measurement of, for example, cationic biocide residuals, such as the QAC and HPLC methods, is that these new systems and methods measure only the amount of free quat versus total quat. Accordingly, the present disclosure allows for the more accurate measurement of the amount of anti-microbially active cationic biocide present in an industrial water stream and can also quantify the amount of cationic surfactant and cationic polymer present in an industrial water stream.